An evaporative pattern casting is a kind of casting method, and may be called a lost-foam casting or a full mold casting. This method may be generally described as below. First, a pattern is made of an evaporative material which evaporates by heat of a molten metal. The pattern is called an evaporative pattern. Next, a sand mold is made by burying the evaporative pattern therein. The molten metal is poured into a cavity of the sand mold. Here, the ‘cavity’ means a space which is occupied by the evaporative pattern in the sand mold. When the molten metal is poured into the cavity, the evaporative pattern evaporates by the heat of the molten metal, and the space which is occupied by the evaporative pattern is filled with the molten metal. When the sand mold is broken down after the molten metal is cooled and solidified, a casted structure perfectly having the same shape as that of the evaporative pattern is obtained. As the evaporative material, foam polystyrene or wax is typically used.
The evaporative pattern is designed by using a computer aided design (CAD). In general, the CAD is used for designing various structures. An efficient CAD technique using the characteristics of a design subject may be proposed. For example, the patent document 1 discloses a CAD technique appropriate for designing an iron rod unit.